This invention relates to a monolithic integrated threshold switch and, more particularly, to a monolithic integrated circuit of I.sup.2 L design.
This design principle, the "integrated injection logic" (I.sup.2 L)--cf. "Philips Techn. Rev.", 33, No. 3 (1973), pp. 76 to 85--is also referred to as "merged transistor logic"--cf. "1972 IEEE International Solid-State Circuits Conference", Digest of Technical Papers, pp. 90 to 93. The main features of this design principle are collector regions lying at the semiconductor surface, and injectors which are common to a plurality of transistors and, as part of a lateral transistor structure, control the current flow in the vertical transistors and serve as current sources. The injector can be represented in the equivalent circuit diagram as an equivalent transistor whose base is at the emitter potential of the respective vertical transistor, and whose collector is connected to the base of this vertical transistor. The collector region of the equivalent transistor is identical with the base region of the vertical transistor. For clarity, these equivalent transistors corresponding to the injectors have been omitted in the accompanying drawing.
The advantages of the integrated injection logic lie in the fact that relatively little semiconductor surface is required, and that it is easy to realize digital circuits with multicollector transistors by the normal planar diffusion technique without resistors and capacitors. Furthermore, no special current sources are required for the transistors, which are supplied with current via the injectors. Since, moreover, the individual transistors can be provided with electrically isolating regions to reduce the semiconductor surface required, it is desirable to have circuits which can readily be combined with a monolithic integrated circuit of I.sup.2 L design, particularly circuits whose emitters are at a common potential.